THERMAL STRUCTURE AND RHEOLOGY OF UPPER-MANTLE BENEATH ZHEJIANG PROVINCE, CHINA

The paleogeotherm derived from spinel and garnet lherzolites xenoliths for the upper mantle beneath Zhejiang Province, China is higher than the oceanic geotherm but is similar to the geotherm for the upper mant le beneath eastern China constructed by Xu et al. and the upper mantle geotherm of southeastern Australia. The crust-mantle boundary defined by this geotherm is about 34 km, while the lithosphere-asthenosphere boundary is about 75 km. This result coincides well with geophysical d ata. The study of rheological features of the xenoliths has revealed t hat at least two periods of deformation events occurred in the upper m antle beneath this region. The first event might be related to upper m antle diapir occurring in this region before or during late Tertiary, and che second might be related to the occurrence of small-scale shear zones in the upper mantle.